Shares of BioDelivery Sciences International surged Monday before markets opened and after the drug developer said its potential severe pain treatment fared better than a placebo, or fake drug, in another late-stage study.

The Raleigh, North Carolina, company said the trial also triggered another $10 million milestone payment from Endo International Plc, which has a licensing agreement with BioDelivery.

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The drugmaker said its treatment, BEMA buprenorphine, led to significantly improved chronic pain relief when compared to a placebo in patients who had tried other opiates. The drug is being developed to manage pain that is bad enough to require daily, around-the-clock, long-term opioid treatment. Nausea and vomiting were the most common side effects in patients treated with the drug.

BioDelivery also had said in January that the experimental drug fared better than a placebo in another late-stage study of patients who hadn't had an opioid treatment. That study also triggered a $10 million milestone payment from Endo.

Late-stage research is the last and most expensive testing phase to which a drug is submitted before being sent to federal regulators for approval. BioDelivery said it will meet with Food and Drug Administration officials this month and then prepare and submit its drug application as soon as possible.

A spokeswoman said approval of the drug could yield up to $50 million in additional milestone payments.

BioDelivery Sciences International Inc.'s stock price spiked nearly 21 percent, or $2.49, to $14.48 more than an hour before markets opened.